Thermoplastic elastomers are known. They have many of the properties of thermoset elastomers, yet they are processable as thermoplastics. One type of thermoplastic elastomer is a thermoplastic vulcanizate, which may be characterized by finely-divided rubber particles dispersed within a plastic. These rubber particles are crosslinked to promote elasticity.
For example, U.S. Pat. No. 4,803,244 teaches the preparation of thermoplastic elastomers by admixing, under reaction conditions, an unsaturated elastomer containing carbon-carbon double bonds, an essentially saturated thermoplastic polymer, a multifunctional organosilicon compound containing an average of at least two Si—H groups per molecule, and a catalyst capable of hydrosilylating the carbon-carbon double bonds of the unsaturated elastomer. Examples of multi-functional organosilicon compounds include polymethylhydrodimethylsiloxane copolymers terminated with trimethylsiloxy groups or alkoxy groups; polymethylhydrosiloxane polymers similarly terminated; polymethylhydrodimethylsiloxane methylsiloxane terpolymers similarly terminated; bis(dimethylsilyl)benzene; bis(dimethylsilyl)alkanes; and silicone fluids, provided that they contain an average of at least two Si—H groups per molecule.
U.S. Pat. No. 5,672,660 teaches improved thermoplastic vulcanizates prepared by dynamic curing—through hydrosilation—in the presence of a platinum-containing catalyst, a diene-containing rubber having predominantly sterically unhindered carbon-carbon double bonds. For example, the diene-containing rubber may include units deriving from 5-vinyl-2-norbornene, which provides an unhindered carbon-carbon double bond. The patent further teaches the use of hydrosilating agents, which include at least two silicon hydride groups, such as methylhydrogen polysiloxanes, methylhydrogen dimethylsiloxane copolymers, alkyl methyl polysiloxanes, bis(dimethylsilyl)alkanes and bis(dimethylsilyl)benzene.
Unfortunately, the availability of diene-containing rubbers that include desirable unhindered carbon-carbon double bonds is limited. For example, ethylene-propylene rubbers containing units deriving from 5-vinyl-2-norbornene are not widely available, especially where the rubber includes significant levels of diene incorporation. While ethylene-propylene rubbers containing diene units deriving from 5-ethylidene-2-norbornene are more widely available, the ability to cure these rubbers by way of hydrosilation, particularly when dynamically vulcanizing rubber to form a thermoplastic vulcanizate, requires a significant amount of platinum catalyst, which can be disadvantageous due to the costs associated with the catalyst. There is therefore a desire to develop technology to more efficiently hydrosilate widely available ethylene-propylene rubbers, such as those containing units from 5-ethylidene-2-norbornene.
Hydrosilating agents have also been employed to cure unsaturated rubbers to form thermoset compositions. For example, U.S. Pat. No. 6,972,309 teaches curable compositions made by blending polyisoprene rubber with a hydrosilation catalyst and a crosslinking agent. The crosslinking agent includes at least two hydrosilyl groups per molecule and may be defined by the formula
wherein n represents an integer from 1 to about 3 and R represents an alkyl group containing from 1 to 4 carbon atoms, a phenyl group, or a hydrosilyl group. The use of these crosslinking agents does not effectively cure sterically hindered vinyl groups like those deriving from 5-ethylidene-2-norbornene. There is therefore a desire to discover or develop a more efficient crosslinking agent for these types of rubbers.